Abstract: In order to explore the pore structure and pore size fractal characteristics of coal rank coal in Permian Longtan Formation of Panjiang Mining Area in southwestern Guizhou,the pore structure was characterized through high pressure mercury injection experiment and low temperature nitrogen adsorption experiment.Moreover,the multi-scale characteristics of the pore structure of medium-rank coal were compared and analyzed based on fractal theory.The findings indicate that the micropores and small pores of medium rank coal in the study area are rather developed,the pore connectivity is good,and the pore fractal characteristics are significant.The comprehensive fractal dimension of medium-rank coal is capable of reflecting more effectively the metamorphic degree of medium-rank coal,and has a certain positive correlation with Langmuir volume and Langmuir pressure.To a certain extent,it reflects the deposition feature and desorption difficulty of coalbed methane,that is,the larger the fractal dimension of medium-rank coal,the more conducive to the development and utilization of coalbed methane.The findings of this study can provide valuable data and theoretical basis for further exploration and development in the field of research.

Key words: medium-rank coal, pore structure, fractal theory, high pressure mercury injection, nitrogen adsorption, Panjiang Mining Area